In a conventional screen controlling apparatus, such as a mobile communication terminal, a portable media player (PMP), a television (TV), or a personal computer (PC), an input device, such as a mechanical key button, a button type remote controller, or a mouse, has been used by a user to control a display screen. Recently, due to the development of a touch sensing technology, almost all of the functions of an image output device may be controlled, without using the conventional input devices, through the user's finger contact with a display panel so that the image output device, such as a smart phone, a tablet PC, or a smart TV, may perform more convenient and more various functions than a conventional terminal.
However, in a pressure sensitive touch sensing technology or a resistive touch sensing technology, touch sensitivity is low. In a capacitive touch sensing technology, it is difficult to control the image output device when the user wears a glove having different capacitance from that of the finger or when the finger is covered with water or a foreign substance. In addition, although touch sensing may be used, repetitive finger contacts with the screen make the user tired and inconvenient. Therefore, a more convenient and simpler input unit for the user is necessary.